Citrullination is the post-translational conversion of peptidyl-arginine to peptidyl-citrulline and is mediated by a family of enzymes known as peptidyl-arginine deiminases (PADs). Citrullination has been demonstrated to be an inflammation-dependent process due to the constitutive expression of the enzymes PAD2 and PAD4 by polymorphonuclear leukocytes as well as cells of the monocytes/macrophage lineage. The link between inflammation and atherosclerosis is well established with numerous mechanisms implicated including oxidative modification of protective HDL proteins induced by the enzyme myeloperoxidase. However, another post- translation modification recently identified within the atherosclerotic plaque is protein citrullination. We have identified several citrullinated plaque proteins including prominently, the HDL-associated protein ApoA-I . ApoA-I facilitates removal of excess cellular cholesterol thus impeding atherogenesis. Additionally, ApoA-I has been demonstrated to have direct anti-inflammatory effects thus limiting vascular inflammation. We propose to study citrullination as a novel mediator of inflammation induced atherosclerotic progression. This work represents a scientific progression of our previous studies demonstrating citrullination within the atherosclerotic plaque. The proposed studies will provide new insights into how a group of enzymes ubiquitously carried by white blood cells, peptidyl arginine-deiminases (PADs), contributes to the effect of pathologic inflammation within the atherosclerotic plaque. The main goal of this application is to investigate the role of ApoA-I citrullination as a risk factor for atherosclerotic development and progression. Specifically, we propose to: 1. Define the sites of ApoA-I citrullination from in-vitro citrullinated ApoA-I as wellas ApoA-I isolated from human plasma, and from within the atherosclerotic plaque; 2. Confirm and characterize citrullination-dependent abrogation of ApoA-I cholesterol efflux capacity and to identify residues critical for mediating this abrogation; 3. Use pharmacologic and genetic animal models to define the role of citrullination in atherosclerosis progression, and 4. Quantitate citrullination of plasma ApoA-I and correlate with subclinical atherosclerosis as well as atherosclerotic events. Success of these studies could identify novel mechanisms contributing to inflammation-driven atherosclerosis and have the potential to both contribute to the development of diagnostic tests for cardiovascular risk prediction, as well as identifying potentia therapeutic targets for the treatment and/or prevention of coronary artery disease.